Field of the Invention
The present invention relates to an image processing apparatus, an image processing method, and a storage medium, and more particularly, to an image processing technique of processing a medical image captured by various kinds of medical image collection apparatuses (modalities) such as a magnetic resonance imaging apparatus (MRI), an X-ray computed tomography apparatus (X-ray CT), and an ultrasonic image diagnostic apparatus (US).
Description of the Related Art
In image diagnosis using medical images (3D tomographic images representing information in an object), a doctor makes a diagnosis while comparing images obtained by a plurality of imaging apparatuses (modalities) based on different positions, times, imaging parameters, and the like. However, since the orientation or shape of the object changes between the images, it is difficult to identify or compare a morbid portion. To solve this problem, registering a plurality of images has been attempted.
As a piece of general input information for registration of a plurality of images, feature points (corresponding points) having a one-to-one correspondence between images are used. Some corresponding points can automatically be identified by image processing. There also exist corresponding points that can hardly be automatically identified because of the influence of a modality difference, object deformation, or the like. In addition, corresponding points automatically identified by image processing are not always points that are correctly anatomically associated. For this reason, an operator such as a doctor sometimes manually performs the identification operation of corresponding points between images while viewing the images. The operator inputs a feature point on one medical image (to be referred to as a reference image hereinafter), and searches for and identifies a position corresponding to the feature point from the other medical image (to be referred to as a target image hereinafter) based on a similarity such as an image appearance. Feature points used for registration include a point that is identified by image processing and is not necessarily reliable and a point that is input by the operator and has reliable association.
Japanese Patent Laid-Open No. 2009-160045 discloses a registration technique using a corresponding point (extracted landmark) automatically identified by image processing and a corresponding point (user landmark) manually identified by an operator. In this technique, the user landmark is weighted more than the extracted landmark, and a plurality of images are registered by linear optimization.
However, both a landmark appropriate as a feature point for registration and a landmark that is not so coexist in the extracted landmarks. In the technique disclosed in Japanese Patent Laid-Open No. 2009-160045, registration is performed such that all extracted landmarks match in almost the same degree. Hence, even if positions that the operator wants to match preferentially match, appropriate registration is not always done in the remaining region.
The present invention has been made in consideration of the above-described problem, and provides an image processing technique capable of performing, in registration between a plurality of images, appropriate registration even in a region other than feature points that an operator wants to match preferentially.